The present invention is directed generally to ink jet printing, and, more particularly, to printing on porous print media with pigment-based ink jet inks.
Ink-jet receiving layers need to absorb the ink vehicle delivered during the printing process. When the ink-receiving layer is applied to non-absorbent substrate, the substrate provides no absorption capacity and as a result, the ink-receiving layer must be the sole absorbing material. To increase the absorbing capacity of the coating, an absorbent precoat has been described in the prior art that serves to increase the capacity of the coating, much as a substrate functions in paper-based ink-jet media.
A top coat is applied to control surface properties such as gloss, tackiness, surface energy, and durability, as well as to function in concert with the adsorbent precoat. In addition, the top coat must be free of defects that would contribute to perceived irregularities or non-uniformities in the coating.
U.S. Pat. No. 5,275,867 describes a two-layer coating and a coating process where a top coat is laminated on the precoat. U.S. Pat. No. 5,605,750 describes a three-layer coating and a coating process where the top coats are applied to the precoat by coating both fluids before drying in a multi-slot hopper or a slide hopper. U.S. Pat. No. 5 5,576,088 describes a two layer coating and a coating process where a top coat is cast coated on a precoat. All these examples describe a process that involves specialized equipment and coatings engineered to be compatible with the processes. In addition, production efficiencies may be lower.
In related application Ser. No. 09/491,642, a process is disclosed and claimed that allows the production of multi-layer coatings in which one or more top coats can be applied to a porous base coat to produce a uniform and defect-free coating layer. Specifically, a process is provided in which a liquid is applied to the base coat prior to top coating such that the air in the base coat is removed prior to top coating. This process can occur in-line with a simple apparatus described therein. An added benefit of this method is that it also allows the possibility of adding functionally or performing chemistry to the coatings after the base coat is dried and before the top coat is applied in a single process. For example, the wetting liquid may contain, but is not limited to, surfactants, pH modifiers, polymers, crosslinkers, pigments, and/or dye stabilizers.
Conventional glossy media have polymer-coated surfaces. The ink penetrates the coating via polymer swelling, which is slow. After the image is printed, the printed surface remains saturated with the vehicle and the dry time is long. With porous media, the ink vehicle quickly absorbs into the porous coating via capillary action and the dry time is short. As demand for faster ink-jet printing increases, faster dry time of the media becomes more important.
Examples of porous glossy print media include (1) a high quality glossy paper, Epson White Film S041072 (an opaque polyester) for use with Epson""s Stylus printer and (2) Accuplot EGF Glossy White Film, available from Mile High Engineering Supply Company (Denver, Colo.).
However, the dot size of pigment-containing inks on porous media has always been low, which results in white spaces between dots, and the image appears to be streaky and non-uniform. Ink and media joint investigations have been made in an effort to increase the dot size. While increasing the dot size of dye-based inks on polymer-coated photopaper can be done by lowering the surface tension of the ink in most cases, such an approach shows little effect with pigment-based inks on porous media.
In particular, in an attempt to improve dot size of pigment-based inks on coated porous print media, the following aspects have been examined: ink drop weight, media coating weight, pigment/binder ratio in the media coating, particle size in the media coating, and surfactants in inks or media. However, all of these experiments showed little effect on dot size.
Thus, there is a need to provide increased dot size of pigment-based inks on porous glossy media, for improved print quality thereon.
It is found that by rewetting coated media, such as film-based media (e.g., Mylar film) and resin-coated papers (e.g., photobase paper), with either a dilute polymer solution or a colloidal silica or colloidal alumina dispersion, the dot size increases compared to the current default dot size when printed with pigment-based inks in a Hewlett-Packard CP-2500 or CP-3500 printer. Examples of polymers suitable for use in the present invention include polyvinyl alcohol and polyvinyl acetate copolymer, polyvinyl pyrrolidone, and other water-soluble polymers such as polyamides, cellulose derivatives, and polethylene oxide. The colloidal silica or alumina dispersion have particle sizes in the range of about 1 to 300 nm.
Specifically, the process of the present invention is directed to applying at least one ink-receiving porous layer to a non-porous substrate. The process comprises:
(a) applying a porous base coat to a surface of the non-permeable substrate, the porous base coat comprising a plurality of pores;
(b) applying a first rewet liquid to the porous base coat;
(c) applying a porous top coat on the porous base coat; and
(d) applying a second rewet liquid to the top coat,
whereby the ink-receiving layer is printable with larger dots of a pigment-base ink than without the second rewet liquid.
No previous efforts are known to increase the dot size on coated porous media printed with pigment inks.